A British man is facing up to 27 years in an US jail after he admitted plotting to rape, kill and eat a child in a dungeon he built at his home. Geoffrey Portway, 40, planned to carry out the horrific attacks in an underground chamber lined with material to muffle any sound.

The basement of his Massachusetts home was equipped with a steel cage, a child-sized home-made coffin, scalpels, butchering kits, freezers and castration tools.

Portway boasted of his intention to lock youngsters in his dungeon in a series of disturbing web chats.

He admitted soliciting the kidnap of a child and distribution and possession of child pornography as part of a plea agreement, the US Attorney's Office said.

The UK citizen now faces between 18 and 27 years in an American prison before he is deported back to the UK, US authorities said.

Detectives said Portway detailed his desire to abduct, sexually abuse, murder and eat children he knew in a string of conversations online.

He used programs such as Skype to communicate with American Michael Arnett over several months, asking him for help with the kidnap and setting out his preferred age range.

Police said records of the conversations revealed that the two men discussed real children - by name and photo - who Arnett claimed to know and have access to.

Detectives discovered a host of disturbing material that showed the men shared child pornography and images of injured, mutilated and dead children.

Federal agents raided Portway's home in Worcester on July 27 last year where they discovered a locked door in the basement.

This led to a second door that opened into Portway's lined dungeon which contained the small makeshift coffin equipped with large speakers covered in wire mesh at one end and fitted with exterior locking devices.

It sat close to a steel cage with multiple locks and a steel table top with steel rings at six points, which police believe was designed to restrain victims.

The dungeon was further kitted out with a chair, a television, and what appeared to be cable access to the internet, officers said.

Outside the room detectives found a chest freezer and an upright freezer, along with some disposable scalpels, the butchering kits, and castration tools.

A spokesman for the US Attorney's Office in the district of Massachusetts said: "This dungeon was described in detail by Portway in recovered chats as a place he intended to use to keep kidnapped children while he sexually abused them and as a place to eventually murder and cannibalise the children."

According to US court documents, Portway solicited several people for help in obtaining a child, including Arnett.

Police believe he began to make inquiries at least as early as 2010 and was informed that Arnett had previously helped others with such requests and had "experience" with the abduction and sexual abuse of children.

Various computers and digital devices containing Portway's child pornography collection were seized when officers raided his home last July.

A forensic examination of the material revealed more than 4,500 pieces of child pornography traded with others online.

They included images and videos which appeared to depict dead children and cannibalism.

Authorities believe Portway was part of a worldwide network of offenders and, in many cases, distributed the material based on the preferences of his contacts.

Under the terms of the plea agreement arranged yesterday, Portway must serve between 216 and 327 months in jail, prior to a lifetime supervised release.

He will be required to register as a level three sex offender - the more serious category under US law which signifies an individual is a threat to public safety - and will be deported after serving his sentence, the US Attorney's Office said.

United States Attorney Carmen Ortiz said: "Clearly, the facts of this case were quite disturbing and we are grateful law enforcement acted when they did.

"I hope that this case sends a clear message that we will prosecute to the fullest extent of the law those who participate in these types of activities.

"Even though criminals attempt to hide in the anonymity provided by the internet, the Department of Justice is committed to aggressively pursuing them to ensure that there is no place to hide."

Arnett has pleaded guilty in Kansas to the sexual exploitation of a child for the purposes of producing child pornography.